Systematic AZD Planning
Systematic AZD solutions can be developed by integrating holistic source reduction planning, including considerations for multiple sources, composite solutions and life cycle process and facility optimization. Nine key considerations for systematic AZD planning are:

1. Is the AZD target a fixed endpoint or an optimization point?
The type of AZD target frames the overall AZD options and the planning approach. A fixed endpoint could be below or beyond the most cost-effective (optimal) AZD target. For example, assume that for a particular wastewater stream, the most cost-effective (life cycle) approach would be to use single-stage reverse osmosis to recycle water and reduce wastewater by 80%. A less-than-optimal AZD target might be to pursue a 50% reduction goal, and a beyond-optimal AZD target might be to pursue a 90% or 100% wastewater reduction goal. These endpoint goals may be based on specific drivers or constraints, such as cost. As zero discharge is approached, the costs for incremental discharge reductions can increase significantly in proportion to the benefits achieved.

2. What tradeoffs are there between point source and more combined reduction strategies?
Point source AZD strategies involve the use of bath or rinse purification systems for individual tanks or sources. Alternative strategies might include combining compatible streams from different processes for purification/recovery. This could include use of single fixed location recovery systems (e.g., centralized reverse osmosis/ion exchange for recycling rinse waters from several process lines). Another combined strategy would be to use a mobile system to perform intermittent purification/recovery of several point sources. For example, a single mobile diffusion dialysis system might be used to purify/recycle several different acid baths. Combined strategies may be more cost-effective, due to economy of scale, unless there are substantially increased plant interface requirements. Point source systems may offer more flexibility, redundancy and reliability.

3. What tradeoffs are there between up-the-pipe pollution prevention and end-of-pipe pollution control?
Up-the-pipe systems can reduce end-of-pipe system requirements. For example, bath purification and water recycling can combine to reduce wastewater treatment system contaminant loading and hydraulic sizing. In-plant systems may also produce byproducts requiring waste treatment or management.

4. What combination of technology, technique and substitution would provide the best overall solution?
Sections 3, 4, 5 and 6 present a range of technologies, techniques and process substitution strategies for AZD. Integrated approaches should be considered as potential improvements over single-approach solutions. These sections cover diffusion dialysis, microfiltration, membrane electrolysis, acid sorption, electrowinning, ion exchange, reverse osmosis, vacuum evaporation, atmospheric evaporation and alternative processes.

5. What future production and facility scenarios should be considered?
AZD solutions should consider overall life cycle and future production and facility needs. Potential future requirements may lead to modified AZD alternatives, or more allowances for change. Defining future scenarios may lead to specific phased implementation plans or decisions to accelerate/delay plans for facility renovation.

6. Are AZD solutions well defined?
Whether dealing with a single-point source, multi-process or overall facility alternatives, all significant impacts should be identified and implemented to define requirements for a comprehensive AZD solution. Those include process byproducts, cross-media impacts, plant interface and utility requirements, operations and maintenance requirements. A particular approach may be able to meet the primary AZD performance requirement (e.g., 90% acid reuse) but may present implementation problems caused by other aspects (air discharge requiring ventilation system, permitting, etc). Comprehensive definition of AZD alternatives is important to identify barriers to implementation.

7. How does the surface finishing process chemistry change with production?
One key dimension is understanding the chemistry for each process step and how the chemistry changes during production cycles, including:

• Transfer or transformation of process chemicals rendering them unavailable for production; and
• Generation of contaminants that reduce the useful life of process chemicals.
  

Changes in process chemistry can necessitate the need to purchase fresh or make-up process bath chemicals. Similarly, the increased volume of waste process baths and rinses requiring treatment results in more waste treatment chemicals and corresponding increases in waste generated.

8. What opportunities are there to use existing systems? New systems?
Enhancements to existing systems may produce significant benefits at low cost and overall effort. Additional capital for new systems may result in overall net beneficial gains in capacity, productivity, reduced wastes, automation and space. Beneficial process changes may also result from eliminating or consolidating processes.